• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.6
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• pp.1257-1268
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• 1989

본 연구에서는 이에 천이와 난류모델을 첨가하여 층류 경계층이 천이를 거쳐 난류 경계층으로 발달해가는 전과정을 해석하려고 한다. 또, 이러한 부분 면파의 특성을 needle contact법에 의하여 측정 포물형이나 완전 Navier-Stokes 방정식을 사용함에 있어서 표면곡률항의 중요성을 보이며, 익형의 선단등 표면곡률이 중요한 영역에서도 적용가능한 수치적 방법을 제시한다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2000.11a
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• pp.36-36
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• 2000

천음속 또는 초음속 유동이 유동장의 하류에서 부여되는 압력조건에 의하여 감속되는 경우나, 유동방향의 갑작스런 변화를 요구하는 물체 혹은 벽면이 존재하는 경우에 발생한 충격파는 벽면을 따라 발생하는 층류 혹은 난류 경계층과 복잡한 상호간섭 (interaction)을 일으켜 충격파에 의한 박리 발생, 충격파 하류에 새로운 충격파 발생, 충격파가 큰 진폭으로 진동하게 되는 현상 등을 발생시킨다. 이러한 간섭현상은 고속유동이 통과하는 유체요소나 유체기기의 성능을 좌우하는 매우 중요한 유동현상으로, 유체기계의 설계 시 사전에 고려되어야 할 중요한 공학적 문제이다.(중략)

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.5
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• pp.367-375
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• 2017

RANS computational analysis was performed on the head of the launch vehicle including the hammerhead nose pairing in the supersonic regime. The two-dimensional axisymmetric analysis was performed by using laminar, fully turbulent and transition models and compared with the experimental data. It was observed that different flow phenomena occurred depending on the Reynolds number. Under the high Reynolds number condition, the boundary layer becomes turbulent, which is not separated from the surface of the launch vehicle. With the low Reynolds number condition, laminar separation bubble was produced due to the separation and reattachment of the boundary layer on the expansion-compression edge of the hammerhead type nose fairing. The three-dimensional computations with the angle of attack showed a fully detached vortical structure due to the laminar separation bubble. It is proved that the turbulent transition should be considered to predict the separation bubble with the Reynolds number.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.10
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• pp.795-803
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• 2015

The boundary layer developing over the suction surface of a first-stage turbine blade for power generation has been investigated in this study. For three locations selected in the region where local thermal load changes dramatically, mean velocity, turbulence intensity, and one-dimensional energy spectrum are measured with a hot-wire anemometer. The results show that the suction-surface boundary layer suffers a transition from a laminar flow to a turbulent one. This transition is confirmed to be a "separated-flow transition", which usually occurs in the shear layer over a separation bubble. The local minimum thermal load on the suction surface is found at the initiation point of the transition, whereas the local maximum thermal load is observed at the location of very high near-wall turbulence intensity after the transition process. Frequency characteristics of turbulent kinetic energy before and after the transition are understood clearly from the energy spectrum data.

• Proceeding of EDISON Challenge
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• 2015.03a
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• pp.585-589
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• 2015

본 연구에서는 이중압축램프의 초음속 유동에서 발생하는 충격파 경계층 상호작용을 EDISON_CFD로 해석하기로 한다. 이중압축램프에선 역압력 구배로 인하여 경계층이 박리가 일어나게 되고 박리된 경계층이 다시 이중압축램프에 부착되어 생겨난 박리영역을 관찰할 수 있다. 박리영역의 앞뒤로 유동의 방향이 바뀌게 되면서 압축 팬(compression fan)과 재부착 팬(reattachment fan)이 충격파를 발생시키고 이중압축램프전방의 충격파와 만나서 복잡한 유동 구조를 가지게 됨을 확인하였다. 이와 같은 층류에서 난류, 박리와 재부착의 영역에서의 해석하기 위해선 해석자의 난류모델이 중요하다. $15^{\circ}-30^{\circ}$, $15^{\circ}-45^{\circ}$의 두 종류의 이중압축램프를 $k-{\omega}$ SST 난류 모델과 ${\gamma}-Re_{\theta}$ 천이 모델로 계산을 EDISON_CFD로 수행하였다. 난류 모델의 차이를 표면마찰계수, 압력계수, 마하수로 비교하여 차이점을 분석하였다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.10
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• pp.1-11
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• 2004

An experimental study was carried out to investigate the influence of flow conditions of a boundary layer on the near-wake of a flat plate. Various attaching positions of tripping wires were selected to change flow conditions on a boundary layer. Laminar, transitional, and turbulent boundary layer conditions at 0.98C from the leading edge are imposed to investigate the evolution of symmetric and asymmetric wake. An x-type hot-wire probe(55P61) is employed to measure at 8 stations of the near-wake region. Measured mean velocity distributions are presented in terms of similarity parameter. It is found that the symmetric wake collapses well to the universal profile in the central part of the wake. However, the universal profile is not suitable in describing an asymmetric wake.

• Fire Science and Engineering
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• v.22 no.3
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• pp.188-193
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• 2008

Numerical simulation was carried out for a propane fire of mass transfer rate 3g/m^2-s$ on a 1m high vertical wall. The objectives of this study are to confirm the outcomes of evaluation of the simulator through simulation of natural convection, and to compare the results of the wall fire with those of previous studies. It was confirmed that the simulated boundary layer was laminar at C_s=0.2$ while it was turbulent at C_s=0.1$. The z direction velocity showed lack of turbulent mixing as seen in the natural convection case, and the profiles of temperature and velocities were in relatively good agreement with those of experiment and previous simulation. It was found that the air entrainment into the boundary layer was well predicted.

• Journal of the Korean Society of Propulsion Engineers
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• v.5 no.2
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• pp.8-15
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• 2001

In the continuing quest for increased turbomachinery efficiency, the part played by blade profile shape remains crucial. The application of a heated thin metallic film with CTA(constant temperature anemometer) to the measurements of the laminar and turbulent boundary layer behavior(shock-boundary layer-interaction) in a transonic wind tunnel. Results of measurements with hot-film sensors on transonic compressor blades are extremely difficult to interpret because of ambiguous probe signals due to the complexity of the local flow pattern. In order to get the explicit information and give the designer to interpret characteristic signals from hot-film probes, a method was developed by comparing the results with other measuring technic results.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.7
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• pp.945-956
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• 2000

The axisymmetric bodies considered in this study have hemispherical and ellipsoidal noses. The near-field pressure fluctuations over each nose model at $Re_D=2.43{\times}10^5$ were investigated in the laminar separation region and developing turbulent boundary layers using a 1/8' pin-holed microphone sensor. The wall pressure fluctuations were also measured in an axisymmetric boundary layer on a cylinder parallel to mean flow at a momentum thickness Reynolds number of 850 and a boundary layer thickness to cylinder radius ratio of 1.88.

• Proceeding of EDISON Challenge
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• 2016.11a
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• pp.74-77
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• 2016

본 연구에서는 Scream Jet Intake에 발생하는 충격파 경계층에서 속도를 Supersonic에서 Subsonic으로 줄였을 때의 상호작용을 EDISON_CFD로 해석하기로 한다. 이상적인 공기 유동에서 충격파 경계층의 각도를 $15^{\circ}{\sim}20^{\circ}$, $25^{\circ}{\sim}30^{\circ}$, $15^{\circ}{\sim}40^{\circ}$, $25^{\circ}{\sim}50^{\circ}$와 같이 두 개($5^{\circ}$, $25^{\circ}$)의 각도 차이를 두어 이중압축램프에서의 유동현상을 EDISON_CFD로 수행하고 분석하였다.